8 Titration of Acids and bases

Transcription

1 8 Titration of Acids and bases Name: Date: Section: Objectives Reinforce acid-base chemistry principles from chapter 4 in Silberberg Standardize a sodium hydroxide solution Determine the molarity of an unknown hydrochloric acid solution Understand the use of indicators in titrations Learn proper pipetting technique Learn to titrate a strong acid with a strong base Pre-Laboratory Requirements Read chapter 4.4 in Silberberg Watch the instructional videos on pipetting and titrating Pre-lab questions (if required by your instructor) Laboratory notebook prepared before lab (if required by your instructor) Safety Notes Eye protection must be worn at all times. Hydrochloric acid and sodium hydroxide are caustic and should not come in contact with your skin or clothing. Wear gloves when handling these chemicals. A lab coat or lab apron is recommended. Discussion Chemical analysis addresses interesting questions in the world around you and the nature of these questions is boundless. Is on our water safe to drink? Is the correct amount of medication present in the prescription I received from the pharmacist? These are just two examples of the type of questions that are answered every day by analytical chemists. Titration describes a process where the concentration of an unknown substance is determined by comparing it with a solution of known concentration. The concept that makes titrations possible is finding the equivalence point, i.e., identifying when the quantity of the unknown substance is equal to the quantity of the known substance. The equivalence point is found in a titration by adding trace amounts of a substance, called an indicator, which turns color when the equivalence point is reached. When a strong acid is titrated with a strong base, or vice versa, James Madison University and JMU Board of Visitors

2 the ph of the solution will be about 7.0 at the equivalence point. Phenolphthalein is the indicator used in this experiment. Phenolphthalein is colorless in acidic solutions and turns pink in alkaline solutions. This experiment will be done in two parts: (1) preparation and standardization of a 0.1 M sodium hydroxide solution and (2) determination of the acid concentration in an unknown sample provided by the instructor. Standardization is the process of determining concentration in an unknown solution by titrating it with a solution of known concentration. You should understand the material in chapter 4 of your textbook before beginning this experiment. Pay special attention to the section on Quantifying Acid-Base Reactions by Titration and sample problem 4.7, Finding the Concentration of an Acid from a Titration. (Silberberg, 3 rd ed., pp ). Ionic substances dissociate completely when placed in water. Strong acids are ionic substances that form H + (or more correctly, H 3 O + ) when placed in water and strong bases are ionic substances that form OH - when dissolved in water. (Note: This is the Arrhenius acid-base definition. You will also learn about the Brønsted-Lowry and Lewis acid-base definitions in CHEM 132). Hydrochloric acid, HCl, is the strong acid used in this experiment and sodium hydroxide, NaOH, is the strong base. The approximate concentrations of our solutions will be 0.1 M, and the goal of the experiment is to determine the exact concentration of the unknown acid solution provided by the instructor. Acids contain hydrogen and dissociate in water to give H + : HCl(aq) H + (aq) + Cl - (aq) Bases contain the hydroxyl group and dissociate in water to give OH - : NaOH(aq) Na + (aq) + OH - (aq) An acid (such as HCl) and a base (such as NaOH) react to form water and a salt. In this reaction, we say the acid and the base are neutralized: HCl(aq) + NaOH(aq) Na + (aq ) + Cl - (aq) + H 2 O(l) (balanced equation) H + (aq) + OH - (aq) H 2 O(l) (net ionic equation) Throughout this experiment the NaOH solution will be placed in the buret, and the hydrochloric acid solution will always be in the beaker. The phenolphthalein indicator is colorless in acidic solution, and it will turn pink at the equivalence point. A small excess of OH - is what causes the indicator to change from colorless to pink, which is the titration end point. (Note: You should stop adding NaOH when the solution in the beaker holds a light pink color for about 10 seconds!). Procedure Part I-A: Preparation of 0.1 M Sodium Hydroxide Solution Obtain 50.0 ml of 1 M NaOH in a graduated cylinder and pour it into a clean 500 ml polyethylene bottle. Rinse the graduated cylinder with DI water, pouring the rinse water into the polyethylene bottle. Fill the polyethylene bottle to the shoulder with DI water, leaving a small air space in the bottle to allow thorough mixing when the bottle is shaken. Make certain the cap is tightly secured and shake it to make certain the solution is completely mixed. The bottle now contains a sodium hydroxide solution that is approximately 0.1 M NaOH and must be standardized James Madison University and JMU Board of Visitors

3 Part I-B: Standardization of 0.1 M Sodium Hydroxide Solution Standardization of the sodium hydroxide solution is accomplished by titrating ml of a HCl solution of known concentration. Your instructor will demonstrate the technique for pipetting exactly ml HCl into the Erlenmeyer flask. 1. Rinse your buret twice with about 5 ml of the NaOH solution. 2. Fill the buret with the NaOH solution and position it above an Erlenmeyer flask (Note: be sure there are no air bubbles in the tip of the buret). 3. Obtain a ml pipet and rinse it twice with about 5 ml of the standard HCl solution. 4. Transfer ml of the standardized HCl solution into the Erlenmeyer flask. 5. Add 1-2 drops of phenolphthalein indicator solution into the flask. 6. Record the initial volume of NaOH in the buret before you begin the titration. 7. Begin the titration, swirling the solution in the Erlenmeyer flask as you add NaOH in a drop-wise approach (Note: Your solution will initially turn pink, and then fade back to colorless when swirled. The pink color will remain longer as you approach the end point of the titration). 8. Record the final volume of NaOH in the buret when the solution in the Erlenmeyer flask remains light pink for about 10 seconds. 9. Repeat this procedure two more times, refilling the NaOH in the buret as needed. Molarity of standardized HCl: Trial 1 Trial 2 Trial 3 Volume of HCl delivered from pipet (ml) Initial buret reading (ml) Final buret reading (ml) Volume of NaOH used in titration (ml) Molarity of NaOH (M) Average molarity of NaOH (M) Average deviation of NaOH (M) Relative average deviation of NaOH Reported valued for NaOH solution: ± or ± % Calculations (Note: Use the following relationship to calculate the sodium hydroxide concentration for each trial: (NaOH volume, ml)(m NaOH) = (HCl volume, ml)(m HCl) James Madison University and JMU Board of Visitors

4 Part II-A: Titration of an Unknown Acid The standardized NaOH solution will now be used to determine the concentration of an unknown hydrochloric acid solution. (Note: You are using the same NaOH solution, but a different acidic solution for this part of the experiment!). 1. Since your buret is already clean, there is no need to rinse your buret again with the NaOH solution. 2. Fill the buret with the NaOH solution and position it above an Erlenmeyer flask (Note: be sure there are no air bubbles in the tip of the buret). 3. Obtain a ml pipet and rinse it twice with about 5 ml of the unknown acid solution. 4. Transfer ml of the unknown acid solution into the Erlenmeyer flask. 5. Add 1-2 drops of phenolphthalein indicator solution into the flask. 6. Before you begin the titration, be sure to record the initial volume of NaOH in the buret. 7. Begin the titration, swirling the solution in the Erlenmeyer flask as you add NaOH in a drop-wise approach approach (Note: Your solution will initially turn pink, and then fade back to colorless when swirled. The pink color will remain longer as you approach the end point of the titration). 8. Record the final volume of NaOH in the buret when the solution in the Erlenmeyer flask remains light pink color for about 10 seconds. 9. Repeat this procedure two more times, refilling the NaOH in the buret as needed. Molarity of NaOH (from part I): Unknown number: Trial 1 Trial 2 Trial 3 Volume of unknown acid delivered from pipet (ml) Initial buret reading (ml) Final buret reading (ml) Volume of NaOH used in titration (ml) Molarity of unknown acid (M) Average molarity of unknown acid (M) Average deviation of unknown acid (M) Relative average deviation of unknown acid Reported valued for unknown acid solution: ± or ± % Calculations (Note: Use the following relationship to calculate the unknown acid concentration for each trial: (NaOH volume, ml)(m NaOH) = (unknown volume, ml)(m unknown) James Madison University and JMU Board of Visitors

5 Final Report Your final report should contain the average calculated value for your unknown acid and the unknown number and the average concentration of your sodium hydroxide solution. Be sure to report the correct number of significant figures and the uncertainty of the unknown acid concentration. Attach a sheet to your report containing your calculations. The calculations do not need to be typed, i.e., they can be written by hand if they are legible. References Skoog, D. A.; West, D. M. Fundamentals of Analytical Chemistry; Holt, Rinehart and Winston: New York, 1963; pp Sweeder, R. D.; Jeffery, K. A.; A comprehensive general chemistry demonstration. J. Chem. Ed., 2013, 90, doi: /ed300367y James Madison University and JMU Board of Visitors

Lab Practical: Acid-Base Titration Pre-lab Assignment 1) Potassium hydrogen phthalate (KHP) is a primary standard used to determine the molarity of bases such as NaOH. The equation for this reaction is:

STANDARDIZATION OF A SODIUM HYDROXIDE SOLUTION EXPERIMENT 14 OBJECTIVE The objective of this experiment will be the standardization of sodium hydroxide using potassium hydrogen phthalate by the titration

Experiment 8. Determination of the Molar Mass of an Unknown Acid by Acid-Base Titration In this experiment you will: Prepare and standardize a solution of sodium hydroxide Determine the molecular weight

EXPERIMENT 10: TITRATION AND STANDARDIZATION PURPOSE To determine the molarity of a NaOH solution by titrating it with a standard HCl solution. To determine the molarity of acetic acid in vinegar using

Juice Titration Background Acids in Juice Juice contains both citric and ascorbic acids. Citric acid is used as a natural preservative and provides a sour taste. Ascorbic acid is a water-soluble vitamin

Ascorbic Acid Titration of Vitamin C Tablets Procedure Each Part of lab requires a separate data table. You might want to put each table on a separate page so you can leave room to show equations and calculations.

Analysis of Commerical Antacids Containing Calcium Carbonate Prelab (Week 1) Name Total /10 SHOW ALL WORK NO WORK = NO CREDIT 1. What is the purpose of this experiment? 2. Show the calculation for determining

Chemistry 12 Preparation and Standardization of Acid and Base Solutions, and Testing of Unknowns Abstract A common laboratory procedure is to determine the concentration of an acid or a base solution by

Titration 1 Acid-Base Titrations Molarities of acidic and basic solutions can be used to convert back and forth between moles of solutes and volumes of their solutions, but how are the molarities of these

Experiment: TITRATION OF AN ACID WITH A BASE INTRODUCTION: The word titration is derived from a French word, "titre" which means "to bestow a title upon or to standardize". The purpose of a chemical titration

Ascorbic Acid Titration of Vitamin C Tablets This lab will be completed individually! Make sure you come prepared! Introduction Vitamin C (also known as ascorbic acid, HC6H7O6) is a necessary ingredient

Acid Base Titrations Introduction A common question chemists have to answer is how much of something is present in a sample or a product. If the product contains an acid or base, this question is usually

Experiment 2 Stoichiometry Solids and Solutions Determining the Molarity of a Solution Lab Owl Announcement: Upon completion of this lab, log onto OWL. A Lab Owl section should now appear in your courses

CHEM 311L Revision 2.3 A Volumetric Analysis (Back-Titration) of the Active Ingredient in an Antacid In this laboratory exercise, we will determine the amount of weak base present in an Antacid tablet;

Titration of Aspirin Tablets In this lab, you will determine the percent purity of two commercially available aspiring tablets using an acid-base titration. In general, an acid and a base react to produce

Experiment 20 - Acid-Base Titration: Standardization of KOH and Determination of an Acid Solution In this experiment, you will determine the precise concentration of a weak acid solution that has an unknown

ph Measurement and its Applications Objectives: To measure the ph of various solutions using ph indicators and meter. To determine the value of K a for an unknown acid. To perform a ph titration (OPTIONAL,

Analysis of Hydrogen Peroxide A Redox Titration Introduction Hydrogen peroxide is regarded as an "environmentally friendly" alternative to chlorine for water purification and wastewater treatment. Because

A nalys is of Vinega r Experiment 69 Analysis of Vinegar Problem How can the acid content of vinegar be determined experimentally? Introduction Ordinary "white" vinegar is an aqueous (water) solution of

The Determination of Acid Content in Vinegar Reading assignment: Chang, Chemistry 10 th edition, pages 153-156. Goals We will use a titration to determine the concentration of acetic acid in a sample of

1 Experiment 7: Titration of an Antacid Objective: In this experiment, you will standardize a solution of base using the analytical technique known as titration. Using this standardized solution, you will

EXPERIMENT 12 Prepared by Edward L. Brown, Lee University and Verrill M. Norwood, Cleveland State Community College The student will become familiar with the techniques of titration and expressing a solution

Determination of Citric Acid in Powdered Drink Mixes Citric acid and its salts (sodium citrate and potassium citrate) are found in many foods, drinks, pharmaceuticals, shampoos, and cosmetics. The tartness

Experiment 9 Acidity and Alkalinity of Drinking Water A. Acidity General Discussion While ph is a measure of a water sample's deviation from a neutral value of 7.00, it provides little information about

HASPI Medical Chemistry Lab Objectives 1. Calculate the number of moles of aspirin in each of the tablets 2. Calculate the number of moles of needed to titrate the aspirin 3. Calculate the volume of 0.10M

TITRATION: STANDARDIZATION OF A BASE AND ANALYSIS OF STOMACH ANTACID TABLETS 2009, 1996, 1973 by David A. Katz. All rights reserved. Reproduction permitted for education use provided original copyright

TITRATION: STANDARDIZATION OF A BASE AND ANALYSIS OF STOMACH ANTACID TABLETS 2009, 1996, 1973 by David A. Katz. All rights reserved. Reproduction permitted for education use provided original copyright

ACID-BASE TITRATION LAB PH 2.PALM INTRODUCTION Acids and bases represent a major class of chemical substances. We encounter them every day as we eat, clean our homes and ourselves, and perform many other

The Determination of Hypochlorite in Bleach Reading assignment: Chang, Chemistry 10 th edition, pages 156-159. We will study an example of a redox titration in order to determine the concentration of sodium

Experiment 7 Titration Curves of Strong and Weak Acids and Bases To calibrate a ph probe. To become familiar with acid-base titration curves. To determine the concentration of an unknown acid. Goals Equipment

6 Evaluation of the Gas Law Constant Name: Date: Section: Objectives Measure the value of the gas constant R Use Dalton s Law to calculate the partial pressure of hydrogen in a closed container Learn to

Lab 25. Acid-Base Titration and Neutralization Reactions: What Is the Concentration of Acetic Acid in Each Sample of Vinegar? Introduction Vinegar is basically a solution of acetic acid (CH3COOH). It is

Name Team Name CHM101 Lab Acids and Bases Grading Rubric To participate in this lab you must have splash-proof goggles, proper shoes and attire. Criteria Points possible Points earned Lab Performance Printed

ph: Measurement and Uses One of the most important properties of aqueous solutions is the concentration of hydrogen ion. The concentration of H + (or H 3 O + ) affects the solubility of inorganic and organic

Acid-Base Titration Computer 24 A titration is a process used to determine the volume of a solution needed to react with a given amount of another substance. In this experiment, you will titrate hydrochloric

Acid/Base Basics How does one define acids and bases? In chemistry, acids and bases have been defined differently by two sets of theories. One is the Arrhenius definition, which revolves around the idea

: General Chemistry Lecture 9 Acids and Bases I. Introduction A. In chemistry, and particularly biochemistry, water is the most common solvent 1. In studying acids and bases we are going to see that water

PURPOSE: 1. To determine experimentally the molar solubility of potassium acid tartrate in water and in a solution of potassium nitrate. 2. To examine the effect of a common ion on the solubility of slightly

EXPERIMENT 5 ACID-BASE NEUTRALIZATION AND TITRATION In class we are learning about how a molecule s structure affects its behavior. One special type of behavior is how the molecule responds to water. Water

Lab 7 Titration of Tums The parietal cells in the stomach secrete hydrochloric acid at a concentration of about 0.155 M (ph normally between 2 and 3). The amount of HCl secreted increases when food enters

1 Learning Outcomes EXPERIMENT A7: VINEGAR TITRATION Upon completion of this lab, the student will be able to: 1) Prepare a solution of primary standard 2) Determine the molar concentration of a solution

Alkalinity of seawater Introduction The behavior of carbon in the world's oceans is important to us because of its direct and indirect influence on life. Carbon in the ocean occurs mainly but not exclusively

CH142 Spring 2012 Experiment 3 Weak Acids and Bases After the CSI exemplary kinetics analysis on the decolorization of crystal violet, the tie-dye company has recommended us to one of its business associates,

Balancing Act Teacher Information Objectives In this activity, students neutralize a base with an acid. Students determine the point of neutralization of an acid mixed with a base while they: Recognize

CHM 152 LL, Determining the Identity of an Unknown Diprotic Acid A diprotic acid is an acid that yields two H + ions per acid molecule. Examples of diprotic acids are sulfuric acid, H 2 SO 4, and carbonic

Lab 7 Parts A & B Using Acid/Base Titrations to Measure Vinegar oncentration and the Molar Mass of an Unknown arboxylic Acid hemistry B1A / by Daniel / Summer 2015 Purpose This is a 2 day lab. The first

Acid-Base Titrations Using ph Measurements Introduction According to the Brønsted Lowry definition, an acid is a substance that donates a hydrogen ion and a base is a substance which will accept a hydrogen

Phenolphthalein-NaOH Kinetics Phenolphthalein is one of the most common acid-base indicators used to determine the end point in acid-base titrations. It is also the active ingredient in some laxatives.

Chem 141 Titration Lab Lecture Notes Samuel A. Abrash Q: What is the purpose of this experiment? The purpose of this experiment is to explore two techniques by which we answer the question: How much? One

PURPOSE: To verify a proposed mechanism for the hydrolysis of t-butyl Chloride. PRINCIPLES: Once the Rate Law for a reaction has been experimentally established the next step is its explanation in terms

Volumetric Determination of Chloride Content in Seawater Reading assignment: Chang, Chemistry 10 th edition, pages 151-155. Goals We will measure the chloride content of a sample of local seawater by titration

CHEM 121L General Chemistry Laboratory Revision 3.0 The Determination of Oxalate Ion in Ferric Oxalate Trihydrate using Titrimetry Learn how to perform a quantitative chemical analysis. Learn how to perform

Lab 6 Two Weeks Characterization of Inorganic Compounds* *Taken from an Inorganic Lab course offered at Purdue University Chemical & Engineering News reported the levels of production for industrial chemicals

1 Experiment 17: Potentiometric Titration Objective: In this experiment, you will use a ph meter to follow the course of acid-base titrations. From the resulting titration curves, you will determine the